(1) Field of the Invention
This invention relates to the formation of high contrast alignment marks for patterning highly reflective electrode metal layers and more particularly to the use of back anti-reflection coating material to improve the contrast of alignment marks.
(2) Description of the Related Art
(TSMC-96-120) Ser. No. 08/742,229, filed Oct. 31, 1996by Shih et al. and assigned to the same assignee describes the use of back etching to preserve alignment marks formed in a layer of dielectric.
U.S. Pat. No. 5,401,691 to Caldwell describes a method of forming and preserving alignment marks through integrated circuit processing steps. The invention does not discuss methods of improving the optical contrast of the alignment marks.
U.S. Pat. No. 5,271,798 to Sandhu et al. describes a method for etching localized regions of an integrated circuit wafer to remove tungsten from alignment marks.
U.S. Pat. No. 5,316,966 to Van Der Plas et al. describes a method of forming alignment marks by etching marks into the integrated circuit wafer and filling the etched marks with thermal oxide. The invention does not discuss methods of improving the optical contrast of the alignment marks.
The invention described in this patent application describes a method of forming alignment marks which can be used to pattern a layer of highly reflective electrode metal. The alignment marks cause depressions in the surface of the layer of electrode metal. These depressions are filled with an optically non reflective material thereby greatly increasing the contrast of the alignment marks. The high contrast of the alignment marks makes them highly visible and easy to locate using automatic means.